JPS60173908A - Nonlinear distortion compensating circuit - Google Patents

Abstract

PURPOSE:To compensate a nonlinear distortion of a power amplifier to be compensated over a wide range by controlling at least one saturated level of a linear amplifier and a nonlinear amplifier based on a synthesis signal of the output of both the amplifiers. CONSTITUTION:An input signal from an input terminal 11 is distributed (12) and fed respectively to the linear amplifier comprising an FET13 and the nonlinear amplifier comprising an FET14. The output of the FET13 is fed to a synthesizer 17 via a phase shifter 15 and the output of the FET14 is fed to the synthesizer 17 via an attenuator 16 respectively. The synthesis signal from the synthesizer 17 is distributed (18); one is fed to the power amplifier 21 to be compensated and the other is fed to a control circuit 19. Then the saturation level of the FET14 is controlled by the output of the control circuit 19. Through the forming above, the nonlinear distortion of the power amplifier to be compensated is compensated over a wide range.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field of the Invention The present invention relates to a nonlinear distortion compensation circuit that outputs a compensation signal for compensating for nonlinear distortion of a power amplifier, particularly a high frequency power amplifier such as a microwave band power amplifier.

Prior Art and Problems By connecting a distortion compensation circuit with a characteristic opposite to the nonlinear distortion characteristic to the front stage of a high frequency power amplifier such as a microwave band, even in a nonlinear operation region where the output power of the high frequency power amplifier is large,
It is known to carry out power amplification that compensates for the nonlinear distortion, thereby creating an economical configuration that fully utilizes the output capacity of the high-frequency power amplifier.

For example, as shown in FIG.
A nonlinear distortion compensation circuit is configured by the nonlinear amplifier 4 and the combiner 5, and the input signal applied to the input terminal 1 is distributed by the distributor 2 and applied to the linear amplifier 3 and the nonlinear amplifier 4. an undistorted output signal from amplifier 3;
The output signal containing distortion from the nonlinear amplifier 4 is combined by a combiner 5 and sent from a terminal 6 to a high frequency band power amplifier 7.
The amplified output signal is output from the output terminal 8. The output level and phase of the linear amplifier 3 and the nonlinear amplifier 4 are set so as to obtain a composite output signal from the synthesizer 5 that cancels out the nonlinear distortion characteristics of the power amplifier 7 in the high frequency band.

The output signal of the linear amplifier 3 is A in FIG. 2, and the output signal of the nonlinear amplifier 4 is
If the output signal of is B, then the combined output signal from the combiner 5 will be C. This composite output signal C is adjusted so as to become a compensation signal containing nonlinear distortion with an inverse characteristic for compensating for the nonlinear distortion of the compensated power amplifier. In such a state, when the input signal level increases, the gain of the nonlinear amplifier 4 decreases due to its distortion characteristics, and the output signal phase also changes. Therefore, if the output signal of the linear amplifier 3 is A as in the case described above, the output signal of the nonlinear amplifier 4 will have a magnitude and phase not shown, for example, as B. Thereby, the combined output signal becomes the one shown in C1. If the combined output signal C1 can compensate for the nonlinear distortion characteristics of the uncompensated power amplifier, it will be possible to compensate for the nonlinear distortion of the power amplifier even with changes in the input signal level.

However, the nonlinear distortion characteristics of the power amplifier 7 are often complex, and in particular, power amplifiers in the microwave band are made of GaAs.
It is common to configure a high power amplifier as a multi-stage parallel configuration using microwave band amplification elements such as FETs (field effect transistors). Therefore, it has been difficult to compensate for distortion over a wide range. In addition, when transmitting multilevel orthogonal amplitude modulation signals, the nonlinear distortion characteristics of the power amplifier may cause the transmission band to widen, causing interference, and it is necessary to prevent such transmission band broadening. is requested.

OBJECTS OF THE INVENTION An object of the present invention is to provide a nonlinear distortion compensation circuit that can compensate for nonlinear distortion of a compensated power amplifier over a wide range.

Structure of the Invention The present invention detects a composite output signal of output signals of a linear amplifier and a nonlinear amplifier or an output signal of a compensated power amplifier to control the saturation level of one or both of the linear amplifier and the nonlinear amplifier. It is equipped with a control circuit that
Since the amount of compensation can be controlled in accordance with the input signal level, it is possible to compensate for a wide range of nonlinear distortions. Examples will be described in detail below.

Embodiment of the Invention FIG. 3 is a block diagram of an embodiment of the invention, in which dual gate 1 field effect transistors 13 and 14 are used as the linear amplifier and the nonlinear amplifier. The input signal applied to the input terminal 11 is distributed by the distributor 12 to the field effect transistor 13.1.
4 is added to the first gate. A control signal from a control circuit 19 is applied to the second gate of the field effect transistors 13 and 14. Further, the source is grounded, a phase shifter 15 is connected to the drain of the field effect transistor 13, an attenuator 16 is connected to the drain of the field effect transistor 14, and the signals passed through the phase shifter 15 and attenuator 16 are combined. Vessel 1
7 and synthesized.

When the field effect transistor 13 is a linear amplifier and the field effect transistor 14 is a nonlinear amplifier, the control signal applied to the second gate is set in advance so that the field effect transistor 14 reaches the saturation state earlier, or In combination with this control signal, the distribution ratio of the distributor 12 can be set to increase the distribution to the field effect transistor 14 side. In this case, the combination ratio in the combiner 17 is also set corresponding to the distribution ratio in the distributor 12. In this way, by setting the operating states of the field effect transistors 13, 14 and adjusting the relative phase by the phase shifter 15 and the relative level by the attenuator 16, the combined output by the combiner 17 is obtained. The signal includes a distortion component having a characteristic opposite to that of the nonlinear distortion of the power amplifier 21. The phase shifter 15 and attenuator 16 adjust the phase and level when a compensation signal is formed by combining an undistorted input signal and a distorted input signal.
It is also possible to connect both field effect transistors 13,14.

This combined output signal is applied to a power amplifier 21 via a divider 18 and a variable attenuator 20, and the amplified output signal of the power amplifier 21 is outputted to an output terminal 24 via a divider 22. The amplified output signal distributed by the distributor 22 is applied to a level control circuit 23, and the amount of attenuation of the variable attenuator 20 is controlled so that the level of the amplified output signal is constant. Note that such means for making the amplified output signal level constant may be omitted.

Also, a part of the composite output signal distributed by the distributor 18 is applied to a control circuit 19, which detects the composite output signal level, and
By controlling the saturation level of the field effect transistor 14 constituting the nonlinear amplifier, the amount of distortion generated is changed,
Furthermore, the field effect transistor 13 that constitutes the linear amplifier operates in a linear operation region that is not a saturation region, and by controlling its gain, the compensation signal synthesized by the synthesizer 17 can be changed in accordance with the input signal level. .

That is, even if the nonlinear distortion characteristics of the power amplifier 21, which is a compensated power amplifier, change in response to changes in the input signal level,
A compensation signal corresponding to the change can be output.

FIG. 4 is an explanatory diagram of a frequency spectrum of a multi-value quadrature amplitude modulation signal such as a 16-value CAM (quadrature amplitude modulation) signal, and the center frequency f. When the frequency spectrum when the distortion is small is shown by the solid line, the frequency spectrum broadens as shown by the dotted and chain lines as the nonlinear distortion of the power amplifier increases. Therefore, it is possible to compensate for the nonlinear distortion of the power amplifier by detecting the frequency at which the spectrum spreads, for example, f, f2 components, and forming a compensation signal that strongly reduces this frequency component. .

FIG. 5 is a block diagram of an embodiment of the present invention that detects the aforementioned frequency components and compensates for nonlinear distortion, and shows the power amplifier 2.
1, for the sake of simplicity, the configuration for making the amplified output signal level constant is omitted. 31 is a band-pass filter, 32 is a distributor, and 33 is a band-pass filter. Since it is also possible to connect the band-pass filter 33 instead of the band-pass filter 31, the distributor 32 and the band-pass filter 33 can be connected. is shown by the dotted line. The bandpass filters 31 and 33 have a characteristic that they can extract one or both of the frequencies f, ', and f2 shown in FIG. 4, and apply the extracted signal components to the control circuit 19.

The control circuit 19 detects that when the input signal level increases for one or both of the frequencies r, f, . . . extracted by the bandpass filter 31, the nonlinear distortion of the power amplifier 21 increases, Since the spread of the spectrum becomes large, the second gates of the field effect transistors 13 and 14 are controlled so as to include distortion components having the opposite characteristics.

In addition, as shown by the dotted line, a part of the amplified output signal is distributed by the distributor 32, and a part of the amplified output signal is distributed by the bandpass filter 33 at frequencies r, , f2.
If one or both of them are extracted and added to the control circuit 19, the frequency ft included in the amplified output signal
, fz, or both of the components are controlled to be small. Thereby, an amplified output signal containing no nonlinear distortion is obtained from the power amplifier 21.

FIG. 6 is a block diagram of still another embodiment of the present invention, in which 41 is an input terminal, 42 is a divider, 43, 44 is a single gate field effect transistor, 45 is a phase shifter, and 46 is a block diagram of another embodiment of the present invention. an attenuator, 47 a combiner, 48 a distributor, 49 a control circuit,
50 is a variable attenuator controlled by the control circuit 49; 51
is the output terminal. The distribution ratio of the divider 42 is set so that the field effect transistor 43 operates as a linear amplifier and the field effect transistor 44 operates as a nonlinear amplifier, and the combination ratio of the combiner 47 is also set corresponding to this distribution ratio.

The variable attenuator 50 can be, for example, a pin diode attenuator, and controls the variable attenuator 50 in response to the combined output signal level from the combiner 47 to reduce distortion components included in the combined output signal. The phase, level, etc. of the output terminal 51 are changed in accordance with the nonlinear distortion characteristics of the compensated power amplifier connected to the output terminal 51. Thereby, even if the input signal level changes significantly, it is possible to compensate for the nonlinear distortion of the power amplifier accordingly.

The variable attenuator 50 can also be connected to the gate of the field effect transistor 44 and controlled so that the composite output signal compensates for the nonlinear distortion of the power amplifier.

DETAILED DESCRIPTION OF THE INVENTION As described above, the present invention provides a field effect transistor 1
Detecting the composite output signal of the output signal of the linear amplifier consisting of 3.43 etc. and the non-linear amplifier consisting of field effect transistor 14.44 etc. or the output signal of the compensated power amplifier and detecting which of the linear amplifier and the non-linear amplifier A control circuit 19.49 is provided to control the saturation level of one or both of them, and since the linear amplifier and the nonlinear amplifier can be configured with the same type of transistor, even if a temperature change occurs, Changes in the composite output signal that is input to the compensated power amplifier to compensate for its nonlinear distortion characteristics can be suppressed, and stable nonlinear distortion compensation can be performed. In addition, since the level or spectrum of the synthesized output signal or amplified output signal changes in response to changes in the input signal level, it is possible to detect this and compensate for the nonlinear distortion characteristics of the power amplifier to be compensated. It has the advantage of being able to compensate over a wide range of signal levels.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a conventional nonlinear distortion compensation circuit, FIG. 2 is a vector explanatory diagram of a compensation signal, FIG. 3 is a block diagram of an embodiment of the present invention, and FIG. 4 is an explanatory diagram of a frequency spectrum. 5 and 6 are block diagrams of different embodiments of the present invention. 11.41 is an input terminal, 12.42 is a divider that distributes the input signal, 13.14 is a dual gate field effect transistor, 15 is a phase shifter, 16 is an attenuator, 17.47 is a combiner, 18.48 is a distributor that distributes the composite output signal, 1
9.49 is a control circuit, 20.50 is a variable attenuator, 21 is a power amplifier, 22 is a distributor, 23 is a level control circuit, 2
4 is an output terminal, 31 and 33 are band pass filters, 32
is a distributor, and 43.44 is a field effect transistor. Patent Applicant Fujitsu Ltd. Representative Patent Attorney Shoji Aitani Representative Patent Attorney Hiroshi Watanabe - Figure 1

Claims (1)

[Claims] In a nonlinear distortion compensation circuit that distributes an input signal and inputs it to a linear amplifier and a nonlinear amplifier, and combines and outputs the output signals of the linear amplifier and the nonlinear amplifier to compensate for the distortion characteristics of a compensated power amplifier. , a control circuit that detects a composite output signal of the output signals of the linear amplifier and the nonlinear amplifier or an output signal of the compensated power amplifier to control the saturation level of either or both of the linear amplifier and the nonlinear amplifier. A nonlinear distortion compensation circuit characterized in that: